Fluidized bed reactors are widely used in the chemical industry for manufacturing various materials and can be particularly useful in the manufacture of polyethylene. To ensure efficient operation of a fluidized bed reactor, it is desirable to control operations to keep the level of the fluidized bed as high as possible, while allowing as few solids as possible to escape the fluidized bed reactor. However, controlling the level of the fluidized bed is often difficult because the top of the bed is often not well-defined, which can lead to inaccurate measurements of bed height and result in inefficient operations.
Numerous methods of controlling the level of the fluidized bed have been described over the years, including, for example, using a series of pressure differential taps along the height of the fluidized bed reactor to calculate the fluidized bulk density and estimate the height of the fluidized bed. However, the impulse legs of the pressure taps are often prone to plugging with solids and/or condensable liquids, resulting in inaccurate pressure measurements. Regular purging of the fluidized bed reactor can help prevent or reduce plugging of these pressure taps. However, the purging of the pressure taps results in a temporary loss of bed level indication, which can lead to bed level upsets and increased fines carry-over out of the reactor. These impact reactor production rates, product quality, and in some cases result in reactor downtime, resulting in substantial inefficiencies and higher costs. Further, because the propensity of these pressure taps to plug with solids and/or condensable liquids is known, the level of the fluidized bed in the fluidized bed reactor is often kept at levels significantly lower than the maximum fluidized bed height, in an effort to minimize fines carry over even with inaccurate pressure measurements and bed height calculations.
Accordingly, there is a need for improved methods of measuring and controlling the bed height in fluidized bed reactors.